I actually had both for awhile. I liked the JX-3P better. I guess that the filter chip makes a noticeable difference. One thing I did not like about the JX-3P was no response to midi velocity, which the MKS had.

Later model JX-3Ps can be booted into velocity mode by holding down one of the front panel buttons. Down side is the keyboard is not usable, but if played by MIDI, you get velocity. It makes it a big JX-3P module with velocity.